Added preference_changed web socket event

web/react/dispatcher/event_helpers.jsx

@@ -148,3 +148,10 @@ export function emitClearSuggestions(suggestionId) {
         id: suggestionId
     });
 }
+
+export function emitPreferenceChangedEvent(preference) {
+    AppDispatcher.handleServerAction({
+        type: Constants.ActionTypes.RECIEVED_PREFERENCE,
+        preference
+    });
+}